Design Of Optical System For Star Sensor And Study On Stray Light Suppressing Technology

Star sensor is an important part of the current spacecraft attitude control, the high precision positioning advantage has great prospects for development in the aerospace control. The optical system is an important part of star sensors, more and more in the direction of large diameter, large field of view, high precision and wide spectral. Because the environment star sensor worked is the vacuum of space environment, and the detected targets are faint and small stars, therefore the stray light for target extraction effect of star sensor is very important. Hence stray light suppression of star sensor is needed, so as to ensure the accuracy of the attitude control. This paper is based on the research work above two aspects.First, the development of domestic and alien star sensors and stray light suppression methods, the working principle and main technical index of star sensor are introduced, as well as the analysis methods, analysis steps and suppression methods of stray light.Second, a CMOS chip is chosen because of the target with low energy. This chip will make star sensor has higher resolution and higher accuracy of measurement based on its large number of pixels and small pixel size. The design index of optical system is calculated based on the parameters of detector. The structure of refractive optical system is chosen after comparing the structure of refractive optical system, structure of reflective optical system and structure of catadioptric optical system. Compared with the other two kinds of structures, it has the advantages of large field of view, no central obscuration and compacted structure. Based on the Total Internal Reflection (TIR) principle, the relationship between the first lens and incident light is talked. Then, the relationship among thickness and radius of near-hemisphere and angle of incident light is deduced and an optical system with the near-hemisphere lens as its first lens is designed. Last suppression intention of stray light is reached by optical system itself. The optical system designed in this paper has the characteristics of wide field of view, wide spectral range and small magnification chromatism.Last, the relationship between length of lens hood and angle of incident light is deduced based on the principle of two reflections before stray light get into optical system. Then a lens hood with a cylinder and diaphragm of conical arrangement is designed, and the suppression ability of stray light is analyzed. Because of the long length the first lens hood has, another reflective lens hood is designed. This one, according to stray light evaluation index PST, has shorter length with qualified PST.